Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
Hum - Songwriting for iPhone
GNUitar - GNUitar is guitar effects software that allows you to use your PC as guitar processor.
Tape It - App for songwriting & audio recording.
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.
Songcraft.io - A platform for songwriters to write, organize & collaborate.